An ultrasound system has become an important and popular diagnostic tool since it has a wide range of applications. Specifically, due to its non-invasive and non-destructive nature, the ultrasound system has been extensively used in the medical profession. Modern high-performance ultrasound systems and techniques are commonly used to produce two or three-dimensional diagnostic images of internal features of an object (e.g., human organs).
Generally, the ultrasound image is displayed in a Brightness-mode (B-mode) by using reflectivity caused by an acoustic impedance difference between the tissues of the target object. However, if the reflectivity of the target object is hardly different from those of the neighboring tissues such as tumor, cancer or the like, then it is not easy to recognize the target object in the B-mode image.
To resolve the problem relating to recognizing the tumor, cancer and the like in the B-mode, an ultrasound elastic imaging technology has been developed to visualize mechanical characteristics of the tissues such as the elasticity thereof in the ultrasound system. Such technology is very helpful for diagnosing lesions such as tumor and cancer, which are hardly recognized in the B-mode image. The ultrasound elastic imaging technology may utilize the scientific property that the elasticity of the tissues is related to a pathological phenomenon. For example, the tumor or cancer is relatively stiffer than the neighboring normal tissues. Thus, when stress is uniformly applied, a displacement of the tumor or cancer is typically smaller than those of the neighboring tissues.
The elastic images may be acquired by using a stress applying unit, such as an ultrasound probe, to apply stress to the target object (“first time duration”) and/or release the stress applied to the target object (“second time duration”). If the stress is applied to the target object by using the ultrasound probe, then lateral components in echo signals may be increased due to the motion of the ultrasound probe. Thus, the quality of the elastic image acquired by applying the stress may be lowered than that of the elastic image acquired by releasing the stress. Accordingly, there is a need to adaptively perform persistence processing on the elastic images according to the first and second time durations.